Wheatstone-bridge balancing system



Patented July 6, 1954 WHEATSTONE-BRIDGE BALANCING SYSTEM Guido Wiinsch, Berlin, Germany, assignor to Askania-Werkc A.-G., a corporation of Germany Application October 17, 1950, Serial No. 190,451

Claims priority, application Germany October 29, 1949 2 Claims. 1

This invention relates to adjustable relays transforming feeble fluid pressure impulses into powerful electric currents for fluid control purposes and the like.

A pair of compression carbon rheostats, a lever actuating the same and an adjustably balanced actuatorsystem for the lever are used as vital parts of the novel relay. It is extremely simple but is believed to be quite new to transform pressure impulses into currents by the present combination of actuators, levers and rheostats and thereby to facilitate adjustments of the relay action.

The invention will be understood more exactly upon consideration of two embodiments thereof, hereinafter described and schematically illustrated in the drawing, wherein:

Figure 1 shows a simple relay transforming fluid pressure impulses into electric currents.

Figure 2 shows a similar relay in conjunction with a control arrangement of the stop-andgo type.

Referring first to Figure 1: A pressure responsive device, such as a diaphragm chamber 10!, receives a pressure impulse to be measured from a source (not shown). At the fulcrum I I32 a lever 593 is pivoted, which is actuated by the device liil, subject to a counter-acting pressure applied to the lever by a control compression spring I64, the force of which can be adjusted, and indicated on a scale 85.

Number lot designates a source of electric current, connected with two compression carbon rheostats or carbon piles ifll, lll'i', which. form an electric bridge, and mechanically center the free end of the lever. Both rheostats are slightly compressed or preloaded when the lever is in equilibrium.

In operation a pressure to be measured with electric response is received in the diaphragm chamber I05 and is counteracted by the mechanical pressure of the compression sprin hi4. If and when the fluid pressure reaches and exceeds a certain magnitude, adjustable on scale 185, it begins to counteract the resistance of spring I55 sufiiciently to compress carbon rheostat lfil, shown at right, while reducing pressure on the left carbon rheostat i i. This change in pressure reduces the electric resistance the right compression rheostat Nil and increases the electric resistance in the left compression rheostat ital"; thereby electrically unbalancing the bridge and producing a current in the diagonal I28 of the bridge. The existence or magnitude of such current can serve to actuate an electric receiver 2 device I21, which is included in the circuit formed by the diagonal 129.

The simple system of Figure 1 may be sufficient if the receiver 52! is an electric motor which is expected to run continuously so long as a current of sufiicient magnitude flows in circult 20; that is, so long as a certain pressure exists in the diaphragm chamber. t is possible with a suitable type of motor to increase or decrease the running speed in response to an increase or decrease of pressure in the diaphragm chamber llll.

It is often desired that the motor should run in response to a change in fluid pressure, but come to rest when a control action has taken place. This is another object in the held of fluid con, ols which can be achieved with means of surprising simplicity and efficiency when using compression rheostats. The spring characteristics of this type of rheostat can be utilized, eliminating the need for mechanical connections required and used in other control systems of this type. This can be explained by reference to Figure 2.

In this embodiment the mechanical construction and operation of the diaphragm chamber 2El, lever 203, soring E34 and compression rheostats 291, 237 can be the same as shown and described for the respective parts we, E3, H34, H37, H37, in Figure 1. The electric receiver in this case is a motor reducer 269 which serves to position a fluid control device by linkage 23!. This motor is energized, directly or through a booster 288, by the current flowing in the diagonal 22E of a Wheatstone bridge. The bridge is energized by a source of current 232, has the compression rheostats 28?, 28'? as resistor arms, and uses a potentiometer 26% as proportioning means; this potentiometer being mocha. ically actuated by the motor linkage 23 i.

The potentiometer shifts the zero or balance point of the Wheatstone bridge, simultaneously with the motor operation, thereby furnishing an infinite number of zero pointsone for each pressure in the diaphragm chamber. In order to stop the motor at any such zero point a small partial return stroke of the lever 2533 is required, since the operation of a motor and motoroperated potentiometer Eli is generally concurrent with but inherently lags a few moments behind the operation of the lever 293. It is usual in generally similar fluid. control systems of the static type, to provide for the return stroke of the lever 233 by yielding and resilient linkage between the lever and a control motor like 239,

which linkage produces the same effect as if the compression of the adjusting spring 204 had been increased. In the present system the yielding and resilient character of the compression rheostat, operating with a. slight lead ahead of the responding motor and potentiometer, has the same eiiect; it produces a slight, partial return stroke of the lever 203, sumcient to reestablish equilibrium in the bridge and thereby to stop the motor 209, regulator 23!! and potentiometer 2 l l in their new positions.

Further modifications of the relays described will no doubt occur to persons skilled in the art.

I claim:

1. An adjustable control relay, comprising a lever; a pair of compression rheostats, compressively preloaded by the lever to resiliently load the lever toward a null position; a fluid pressure responsive device to shift the lever in one direction, to an extent correspondin to a fluid 20 pressure; a Wheatstone bridge comprising said rheostats as resistor arms; a control motor controlled by the diagonal of the bridge; and a com- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,740,356 Kane Dec. 17, 1929 2,023,365 Harding Dec. 3, 1935 2,387,795 Isserstedt Oct. 30, 1945 2,411,139 Roy et al. Nov. 12, 1946 2,479,122 Konet Aug. 16, 1949 2,579,648 Chudyk Dec. 25, 1951 

